Field of Invention
The present invention relates to a wavelength converted semiconductor light emitting device.
Description of Related Art
Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
FIG. 1 illustrates an LED described in more detail in U.S. Pat. No. 7,341,878. A semiconductor structure 130 including a light emitting region is attached to ceramic phosphor 52 by interface 56. Contacts 18 and 20 are formed on semiconductor structure 130, which are connected to package element 132 by metal interfaces 134. In some embodiments, all of the layers disposed between package element 132 and ceramic phosphor 52 have a thickness less than 100 microns. Though FIG. 1 illustrates semiconductor structure 130 mounted on package element 132 in a flip chip configuration where both contacts 18 and 20 are formed on the same side of the semiconductor structure, in an alternative embodiment, a portion of ceramic phosphor 52 may be removed such that contact 18 is formed on the opposite side of semiconductor structure 130 as contact 20.
U.S. Pat. No. 7,341,878 teaches that any luminescent material with the desirable properties of phosphors, such as high absorption of light emitted by the primary light emitting layer and high quantum efficiency, may be used to efficiently produce light in the above-described embodiments. Wavelength-converting materials with a large imaginary component of refractive index, k, at wavelengths emitted by the light emitting region and negligible k at the converted wavelength, such as for example some III-V and II-VI semiconductors, may be used in place of phosphors. In particular, in appropriate materials, at wavelengths emitted by the primary light emitting region, k is greater than 0.01, more preferably greater than 0.1, and more preferably greater than 1. A means for extracting light from the luminescent material may be provided, such as texturing, roughening, or shaping.